Introduction

Redgreen is simple resource-failover service designed to provide resilent and robust entrypoints.

Based on Netflix Hystrix library, the service may be used to isolate points of access to entire system, maintaine system availability during emergent shutdowns (deploys, crashes, unexpected restarts), and so forth.

Redgreen is standalone application, so it could be used and integrated within a system at the operational phase, on the fly, no internal changes in a modules of system are required for integration and usage.

At a Glance

Redgreen application is based on the concept of green-red resources bundle.

Main idea of the bundles - a bundle has the one green resource - primary resource that used to handle incoming requests, and several red resources - backup resources that will help, if the primary one was failed.

Redgreen application allow to define a set of resource bundles, and provide interfaces to handle incoming requests using defined resource bundles.

Installation

Note, redgreen application is requred installed JDK 8 for build and JRE 8 for run.

To install Redgreen application from pre-built distribution just download distribution bundle:

wget https://github.com/ametiste-oss/redgreen/releases/download/v0.1.0/ametiste-redgreen-0.1.0-RELEASE.zip
unzip ametiste-redgreen-0.1.0-RELEASE.zip
cd ametiste-redgreen-0.1.0-RELEASE

To install Redgreen application from the source just clone/download repository/sources and run gradle command to build spring-boot application, for example:

wget https://github.com/ametiste-oss/redgreen/archive/v0.1.0.zip
unzip v0.1.0.zip
cd redgreen-0.1.0/
./gradlew installApp
cd ./build/install

After the build was done, the ./build/install directory would contain spring-boot application distribution.

Usage Example

To configure resource bundles just create file application.properties in the distribution directory:

touch ./application.properties

And add several bundles in the format:

redgreen.direct.bundles.[BUNDLE_NAME].[red|green]=[RESOURCE_URI]

Where BUNDLE_NAME - name of the bundle, this name will be used to compose bundle URL later, and RESOURCE_URI - the URI of bundeled resource.

For example ( note, the green resource URL is intentionally broken to demo failover capabilities ):

echo "redgreen.direct.bundles.my-test-bundle.green=http://example.xcom/test-redgreen-pls" >> application.properties
echo "redgreen.direct.bundles.my-test-bundle.red=http://example.com/" >> application.properties

Note, the one green and at least one red resource is required for each bundle. List of red resources could be defined using comma seprated list of strings: http://foo/,http://bar/.

After this you could run redgreen applicaton using run-script from the ./bin directory:

./bin/ametiste-redgreen --spring.config.location=`pwd`/application.properties

Note, by default redgreen application will start on the port 8080, you can change it using spring-boot property --server.port, for example --server.port=9090

Now you can try it, just query the http://127.0.0.1:8080/my-test-bundle URL by a browser or any http client. In the application log ( probably stdout ) you should see the line, that indicates that the green resource was failed:

ERROR 76471 --- [ HystrixTimer-1] o.a.r.a.HystrixSimpleFailoverLine : Green resource failed, performing fallback for: my-test-bundle

but, the red one is done failover process and you should get the content of example.com resource.

Note, only GET, OPTIONS and HEAD request methods are supported, the methods that can change a state of server is out the scope of redgreen application.